Hair cells are epithelial receptor cells that are capable of transducing mechanical stimuli into electrical responses in both auditory and vestibular systems. There are striking morphological, electrophysiological, and molecular differences between hair cells of different organs and within the same organ. In order to understand the greater picture of how different types of hair cells in different organs or in different positions within the same organ function, a great challenge in auditory and vestibular biology is to identify different genes that are differentially expressed between the different cells and correlate these molecular differences with specific hair cell functions. This application describes two sets of experiments to address two distinct problems in hair cell biology, relating to the role molecular heterogeneity plays creating functional diversity. Overlapping and similar technologies will be used to address two distinct questions. What are the differences in gene expression in type I and type II cells? What are the differences in gene expression in cochlear hair cells located in apical versus basal regions? The consequences of differential gene expression will be explored using a variety of techniques, which will depend on the nature of the genes that are identified.